The printed circuit boards of modern computer systems are typically populated with a variety of electrical components, such as integrated circuit ("IC") devices, diodes, capacitors, and resistors. Such components are usually affixed to a given board by means of a solder bond.
After the board has served its useful life, it is often desirable to remove the components from the board so that those components can be used in another application, or so that the board can be sold as scrap without including any components still on it. IC devices are particularly attractive candidates for reclamation because they are usually the most expensive components on the board. Provided they are not damaged prior to or during the removal process, they can be reused.
In a high volume reclamation process, it is desirable to remove all of the components on the board in as little time as possible, as opposed to the removal of only one or two components. Individual component removal is sometimes done when only one, or a few, components are to be reclaimed from a given board.
A number of approaches to component removal have developed. For example, the apparatus shown in U.S. Pat. No. 3,684,151 issued to Burman et al. on Aug. 15, 1972, generally shows using a substantially closed bath of molten solder to cause the solder bonding the component to the board to reflow. According to Burman, the board is positioned above an opening in the bath by means of a template so that the leads of one of the components on the board are exposed to the molten solder bath. The molten solder thereby causes the solder bonding the leads to reflow and the component can be removed. The operator can then move the board into another position by means of the template to position another component over the opening in the bath, and repeat the process.
The apparatus shown in Burman is configured for the removal of one component at a time, which is not consistent with the objectives of high volume component reclamation. Additionally, it has been found that when solder reflow is accomplished by means of exposing a portion of a board to a molten solder bath, any solder which is on the exposed portion of the board tends to retain a patch of molten solder wherever the exposed solder contacted the bath. Eventually, that patch will harden. This approach may not present significant drawbacks to the reclamation of a single component from a board, given that there will only be a relatively small patch of solder on a portion of the board. It does, however, present significant problems when removing many or all components because a far greater portion of the board picks up the solder which adds to the weight of the board.
Another known approach to component reclamation is shown in U.S. Pat. No. 3,879,836, issued to Coffin on Apr. 29, 1975. In this patent, the board is placed in a vessel so that after the solder affixing the leads is made to reflow, a vacuum can be applied to the component side of the board to remove the components. This approach requires the added complexity of having a vacuum chamber, which is capable of establishing a seal between the chamber and the board, and the vacuum apparatus. Furthermore, Coffin shows the processing of only one board at a time, which has a bearing on the throughput of the system.
Yet another approach to component reclamation is shown in U.S. Pat. No. 4,270,260, issued to Krueger on Jun. 2, 1981. According to Krueger an individual printed circuit board is placed on a mounting frame which secures the board while it is exposed to infrared energy to cause the solder joints to reach their melting temperature. After melting temperature is reached, an extraction tool can be used to remove the components. Drawbacks to the approach shown in Krueger are that each component must be manually removed, and the apparatus is shown to accommodate one board at a time.
What is needed is a component reclamation system which is capable of a high volume throughput by processing multiple boards at the same time, and which is reliable and easy to use.